In this paper we propose a new empiricai econometric methodology based on the formal companson of the results obtained from the analysis of two different data bases that share a common base year, a common period and a common temporal aggregation. We selected two recent Spanish export and import functions, namely those proposed by Buisán and Gordo (1994) and Mauleón and Sastre (1994, 199óa) that satisfy these requirements. We study the differences and common aspects of both data bases. When are found surprising results with the econometric evaluation, we give an explanation, in particular with respect to the different long-run estimation procedures. We carry out an encompassing analysis of each of the equations which is a difíicult task given that both dependent variables are different. Therefore, we study the implications of each specification over the other, using different data bases with a common period and base year. In particular, we study the simultaneity and the interaction between imports and exports. We extend the analysis until 1994 and pay special attention to the parameter stability of the models. We believe that this comparative econometric exercise is very informative, and should be carried out more often.

Keywords: export function, import function, long-run elasticities, short-run elasticities, specification tests, parameter stability test, data base comparison.